Quaternary ammonium carboxylate inner salt compositions as controlled activity catalysts for making polyurethane foam

ABSTRACT

A method for preparing a polyurethane foam which comprises reacting an organic polyisocyanate and a polyol in the presence of a blowing agent, cell stabilizer and a catalyst composition which comprises a quaternary ammonium carboxylate inner salt having the following formula I ##STR1## where R 1  -R 3  are independently C 1  -C 12  alkyl, C 5  -C 8  cycloalkyl or a heterocycle, C 6  -C 10  aryl or heteroaromatic. R 1  and R 2  or R 1  -R 3  together with the nitrogen atom can also be part of nitrogen containing ring system such as piperidine, morpholine, triethylenediamine, imidazole, or 1,8-diazabicyclo-[5.4.0]undec-7-ene. R 4  is a divalent R 1 .

This is a division of application Ser. No. 08/001,977 filed Jan. 8, 1993U.S. Pat. No. 5,240,97.

FIELD OF THE INVENTION

The present invention relates to the use of quaternary ammonium salts ascatalysts for producing polyurethanes.

BACKGROUND OF THE INVENTION

In the production of polyurethanes, it is often desirable to control theactivity of the catalyst(s). The effect of controlled catalysis may berealized in improved reactivity profiles, for instance, delayedinitiation or accelerated cure. Such reaction rate control is ofparticular importance to the polyurethane molder, where it is importantthat the polyisocyanate/polyol mixture remain flowable for sufficienttime to fill the mold properly, while maintaining or improving demoldtime. Controlled catalysis can also affect product distributions andsignificantly impact physical properties of the final polyurethane part.

Latent activity is generally achieved through the use of thermallyactivated "blocked" catalysts. An example is the ammonium salt preparedfrom a tertiary amine and a carboxylic acid (U.S. 3,862,150). Thedisadvantage of such a material is mainly corrosivity, but poor masterbatch stability has also been reported. A related structure is preparedfrom triethylenediamine and a glycol borate acid (U.S. 3,193,515; U.S.3,127,404; FR 2,301,554). An ammonium salt of a quaternary borateresults. The advantage of such a catalyst composition is delayedactivity and/or accelerated cure. U.S. 5,086,081 describes reduced odoramine-boron compositions prepared from tertiary amine polyurethanecatalysts and boric acid. These compositions also impart improvedreactivity during the production if polyurethane parts. U.S. 4,542,214describes the composition and synthesis of tertiary amine salts ofsubstituted carbamic and carbonic acids, and their use as delayed actionpolyurethane catalysts.

Latent activity/accelerated cure has been noted for quaternary ammoniumcarboxylate salts prepared from triethylenediamine and ethylene oxide orpropylene oxide in the presence of a protic acid (U.S. 4,904,629; seealso U.S. 4,040,992). Quaternary ammonium carboxylates are generallyknown to catalyze the trimerization of polyisocyanates (U.S. 4,503,226and references cited therein).

Quaternary ammonium areneoxide zwitterions (U.S. 4,335,219) andsulfonium zwitterions (U.S. 4,111,914) have been used as catalysts forpolyurethane reactions.

Quaternary amonium carboxylate inner salts (zwitterions) have beenprepared. The synthesis of (R)-carnitine (Tetrahedron Lett. 1992, 33,1211-1212), betaine products from an anomalous Eschweiler-Clarkereaction (Tetrahedron Lett. 1991, 23, 3847-3848), and betaines derivedfrom amino and hydrazino acids (Tetrahedron 1990, 46, 1911-1922) are

SUMMARY OF THE INVENTION

The present invention provides a composition for catalyzing thetrimerization of an isocyanate and/or the reaction between an isocyanateand a compound containing a reactive hydrogen, e.g. the urethanereaction for making polyurethane. The catalyst composition consistsessentially of a quaternary ammonium carboxylate inner salt, preferablysuch salt of the following formula I: ##STR2## where R₁, R₂ and R₃ areindependently C₁ -C₁₂ alkyl, C₅ -C₈ cycloalkyl, C₆ -C₁₀ aryl, or suchalkyl, cycloalkyl or aryl group containing a heteroatom. R₁ and R₂ orR₁, R₂ and R₃ together with the nitrogen atom can also compose anitrogen containing C₃ -C₁₂ ring system. R₄ is a divalent R₁, Preferredcatalyst compositions comprise R₁, R₂ and R3 together with the nitrogenatom composing triethylenediamine and R₄ being a C₁ -C₁₂ alkylene group.

As an advantage of these catalyst compositions there is a significantimprovement in reactivity during the production of a polyurethane. Mostnotably, these materials provide delayed initiation. They areunexpectedly potent after being activated and can provide acceleratedcure rates.

DETAILED DESCRIPTION OF THE INVENTION

The catalyst compositions according to the invention can catalyze (1)the reaction between an isocyanate functionality and an activehydrogen-containing compound, i.e. an alcohol, a polyol, an amine orwater, especially the urethane (gelling) reaction of polyol hydroxylswith isocyanate to make polyurethanes and the blowing reaction of waterwith isocyanate to release carbon dioxide for making foamedpolyurethanes, and/or (2) the trimerization of the isocyanatefunctionality to form polyisocyanurates.

The polyurethane products are prepared using any suitable organicpolyisocyanates well known in the art including, for example,hexamethylene diisocyanate, phenylene diisocyanate, toluene diisocyanate("TDI") and 4,4'-diphenylmethane diisocyanate ("MDI"). Especiallysuitable are the 2,4- and 2,6-TDI's individually or together as theircommercially available mixtures. Other suitable isocyanates are mixturesof diisocyanates known commercially as "crude MDI", also known as PAPI,which contain about 60% of 4,4'-diphenylmethane diisocyanate along withother isomeric and analogous higher polyisocyanates. Also suitable are"prepolymers" of these polyisocyanates comprising a partially prereactedmixture of a polyisocyanates and a polyether or polyester polyol.

Illustrative of suitable polyols as a component of the polyurethanecomposition are the polyalkylene ether and polyester polyors. Thepolyalkylene ether polyols include the poly(alkylene oxide) polymerssuch as poly(ethylene oxide) and poly(propylene oxide) polymers andcopolvimiers with terminal hydroxyl groups derived from polyhydriccompounds, including diols and trials; for example, among others,ethylene glycol, propylene glycol, 1,3-butane diol, 1,4-butane diol,1,6-hexane diol, neopentyl glycol, diethylene glycol, dipropyleneglycol, pentaerythritol, glycerol, diglycerol, trimethylol propane andlike low molecular weight polyols.

In the practice of this invention, a single high molecular weightpolyether polyol may be used. Also, mixtures of high molecular weightpolyether polyols such as mixtures of di- and trifunctional materialsand/or different molecular weight or different chemical compositionmaterials may be used.

Useful polyester polyors include those produced by reacting adicarboxylic acid with an excess of a diol, for example, adipic acidwith ethylene glycol or butanediol, or reacting a lactone with an excessof a diol such as caprolactone with propylene glycol.

In addition to the polyether and polyester polyols, the masterbatches,or premix compositions, frequently contain a polymer polyol. Polymerpolyols are used in polyurethane foam to increase the foam's resistanceto deformation, i.e. to increase the load-bearing properties of thefoam. Currently, two different types of polymer polyols are used toachieve load-bearing improvement. The first type, described as a graftpolyol, consists of a triol in which vinyl monomers are graftcopolymerized. Styrene and acrylonitrile are the usual monomers ofchoice. The second type, a polyurea modified polyol, is a polyolcontaining a polyurea dispersion formed by the reaction of a diamine andTDI. Since TDI is used in excess, some of the TDI may react with boththe polyol and polyurea. This second type of polymer polyol has avariant called PIPA polyol which is formed by the in-situ polymerizationof TDI and alkanolamine in the polyol. Depending on the load-bearingrequirements, polymer polyors may comprise 20-80% of the polyol portionof the masterbatch.

Other typical agents found in the polyurethane foam formulations includechain extenders such as ethylene glycol and butanediol; crosslinkerssuch as diethanolamine, diisopropanolamine, triethanolamine andtripropanolamine; blowing agents such as water, methylene chloride,trichlorofluoromethane, and the like; and cell stabilizers such assilicones.

A general polyurethane flexible foam formulation having a 1-3 lb/ft³(16-48 kg/m³) density (e.g., automotive seating) containing the catalystcomposition according to the invention would comprise the followingcomponents in parts by weight (pbw):

    ______________________________________                                        Flexible Foam Formulation                                                                        Parts by Weight                                            ______________________________________                                        Polyol             20-80                                                      Polymer Polyol     80-20                                                      Silicone Surfactant                                                                                1-2.5                                                    Blowing Agent        2-4.5                                                    Crosslinker        0.5-2                                                      Catalyst           0.5-2                                                      Isocyanate Index 70-115                                                       ______________________________________                                    

A general polyurethane microcellular foam formulation having a 12-40lb/ft³ density (192-640 kg/m³), e.g., shoe sole, integral skin,containing the catalyst composition according to the invention wouldcomprise the following components in parts by weight (pbw);

    ______________________________________                                        Microcellular Foam Formulation                                                                    Parts by Weight                                           ______________________________________                                        Polyol              85                                                        Silicone Surfactant 0.1-1                                                     Blowing Agent       0.1-2                                                     Chain extender        1-10                                                    Catalyst            0.5-4                                                     Isocyanate Index 80-120                                                       ______________________________________                                    

The urethane catalyst composition consists essentially of a quaternaryammonium carboxylate inner salt of the following formula I ##STR3##where R₁, R₂ and R₃ are independently C₁ -C₁₂ alkyl, C₅ -C₈ cycloalkyl,C₆ -C₁₀ aryl or such alkyl, cycloalkyl or aryl group containing aheteroatom such as a nitrogen or oxygen. Either R₁ and R₂ or R₁, R₂ andR₃ together with the nitrogen atom can be a nitrogen containing ringsystem which may contain a heteroatom such as nitrogen or oxygen and/ora hydroxy functionality. R₄ is a divalent R₁, i.e., C₁ -C₁₂ alkylene, C₅-C₈ cycloalkylene or C₆ -C₁₀ arylene.

Suitable R₁, R₂ and R₃ groups on the nitrogen would include, forexample, methyl, ethyl, propyl, butyl, lauryl, N,N-dimethylaminoethyl,N,N-dimethylaminopropyl and the like; cyclopentyl, cyclohexyl and thelike; and phenyl, p-tolyl and the like. Illustrative nitrogen containingring systems formed by the nitrogen atom with the R₁ and R₂ groups orthe R₁, R₂ and R₃ groups would comprise, for example, piperidine,morpholine, triethylenediamine, 3-quinuclidinol, imidazole or1,8-diazabicyclo-[5.4.0]undec-7-ene.

Illustrative carboxyorgano groups (--R₄ --CO₂.sup.⊖) on the nitrogenatom of Formula I would include, for example, carboxymethyl (R₄ is --CH₂--), carboxyethyl (R₄ is --CH₂ CH₂ --), carboxypropyl (R₄ is --CH₂ CH₂CH₂ --), carboxyphenyl (R₄ is -C₆ H₄ --) and the like.

Exemplary of quaternary ammonium carboxylate inner salt catalysts arethe zwitterionic reaction products of tertiary amines and haloalkylcarboxylates such as sodium chloroacetate, sodium 3-bromopropionate,tetra-n-butylammonium chloroacetate and the like; lactones such asγ-butyrolactone, β-propiolactone and the like; and unsaturatedcarboxylic acids or carboxylates such as acrylic acid, sodium acrylateand the like. Suitable tertiary amines in these reactions include, forexample, trimethylamine, dimethylcyclohexylamine, triethylenediamine,quinuclidine, 3-quinuclidinol, imidazole, morpholine,1,8-diazabicyclo-[5.4.0]undec-7-ene and the like.

Also exemplary of suitable catalysts are amino acid betaines obtained byalkylation of the amino acid nitrogen. These would include, for example,glycine betaine, γ-butyrobetaine, carnitine, trigonelline, stahydrine,4-hydroxyproline betaine and the like.

A catalytically effective amount of the catalyst composition is used inthe polyurethane formulation. More specifically, suitable amounts of thecatalyst composition may range from about 0.01 to 10 parts per 100 partspolyol in the polyurethane formulation.

In addition, the quaternary ammonium carboxylate inner salt catalystcompositions may be used in combination with other tertiary amine,organotin, and carboxylate urethane catalysts well known in the urethaneart.

These catalyst compositions have the advantage of improved reactivityduring the production of a polyurethane. Most notably, these materialsprovide delayed initiation. They are unexpectedly potent after beingactivated and can provide accelerated cure rates.

EXAMPLE 1

This example shows the preparation of a zwitterion product fromtriethylenediamine and tetra-n-butylamonium chloroacetate. Thetetra-n-butylammonium chloroacetate was prepared from chloracetic acid(1.9 g; 20 mmole) and tetra-n-butylammonium hydroxide (20 mL of a 1.0 Mmethanolic solution; 20 mmole) in solvent tetrahydrofuran (20 mL).Triethylenediamine (2.2 g; 20 mmole) was added and dissolution occurredwithin several minutes. A white precipitate formed over 20 hr. Theprecipate was collected and dried to afford 1.6 g of the zwitterionproduct 1 as a white powder. An additional 1.0 g of product was isolatedfrom the filtrate and dried. The second crop was estimated to be 96%pure (contaminated with tetra-n-butylammonium chloride) by ¹ H NMRanalysis. ##STR4##

EXAMPLE 2

This example shows an alternate preparation of the zwitterion 1 fromtriethylenediamine and sodium chloroacetate. Triethylenediamine (56 g;50 mmole) was dissolved in ethylene glycol (100 g) in a water cooledvessel. Sodium chloroacetate (58 g; 50 mmole) was added in six portionsover 3 hr maintaining an internal reaction temperature of 68-70C. Afterstirring for an additional 72 hr, the sodium chloride was removed byfiltration. Analysis of the ethylene glycol solution showed 51 wt%ethylene glycol, 40 wt% zwitterion 1, 1.4 wt% bis-zwitterion 2, 1.7 wt%triethylenediamine, and 5.7 wt% sodium chloride. ##STR5##

EXAMPLE 3

This example shows the preparation of a zwitterion product fromtriethylenediamine and tetra-n-butylammonium 3-bromopropionate. Thetetra-n-butylammonium 3-bromopropionate was prepared from3-bromopropionic acid (3.0 g; 20 mmole) and tetra-n-butylammoniumhydroxide (20 mL of a 1.0 M methanolic solution; 20 mmole) in solventtetrahydrofuran (20 mi). Triethylenediamine (2.2 g; 20 mmole) was addedand dissolution occurred within several minutes. Minimal precipitationoccurred after stirring for 20 hr. The reaction solution was trituratedwith diethyl ether (60 mL) and the product was filtered and dried toafford 1.2 g of the zwitterion product 3 as a white powder. The productpurity was estimated to be 96% by ¹ H NMR (contaminant wastetra-n-butyl-ammonium chloride). An additional 0.9 g of product wasisolated from the filtrate and dried. The second crop was estimated tobe 92% pure by ¹ H NMR. ##STR6##

EXAMPLE 4

This example shows the preparation of a zwitterion product fromtriethylenediamine and γ-butyrolactone. Triethylenediamine (21 g; 185mmole) was combined with y-butyrolactone (99 g; 1150 mmole) and heatedto 90° C. for 60 hr during which time a precipitate formed. The reactionwas cooled, filtered and the product dried to afford 26 g of thezwitterionic product 4 as a white powder. ##STR7##

EXAMPLE 5

This example shows the preparation of a zwitterion product from3-quinuclidinol and y-butyrolactone. 3-Quinuclidinol (1.29 g; 10 mmole)was combined with γ-butvrolactotie (6.2 g; 72 mole) and heated to 85° C.for 7 hr during which time a precipitate formed. The reaction wascooled, filtered and the product dried to afford 1.0 g of thezwitterionic product 5 as a white powder. ##STR8##

EXAMPLE 6

This example shows the relative rise height vs time for flexible foamsprepared using Example 1 and Example 4 zwitterions in combination withtriethylenediamine. A polyurethane foam formulation premix was preparedfrom the following in parts by weight (pbw):

    ______________________________________                                        Voranol CP6001 (EO-tipped polyether polyol)                                                              100 pbw                                            Diisopropanolamine (85 wt % in water)                                                                    1.0 pbw                                            Goldschmidt B4113 (silicone surfactant)                                                                  1.0 pbw                                            ______________________________________                                    

Control foams were prepared using 0.8 parts per hundred parts polyol(pphp) and 0.5 pphp DABCO 33-LV® catalyst (33 wt% TEDA in DPG). For thezwitterion catalyzed foams, an equimolar amount of zwitterion was usedto replace 0.3 pphp of the DABCO 33-LV catalyst in the 0.8 pphp DABCO33-LV catalyst control foam. For each foam, catalyst (as specified inTable 1) and water (enough to bring the total system water to 2.9 pphp)were added to 135.9 g of above premix in a 5.increment. (12.7 cm)diameter, 10.increment. (25.4 cm) tall paper can and the formulation wasmixed well for 20 sec. Sufficient diphenylmethane diisocyanate (MondurMR; 31.5% NCO) was added to make a 100 NCO index foam (NCO index=moleNCO/mole active hydrogen×100) and mixed well for 4 sec. The foam wasallowed to rise freely, monitoring foam height with time.

                  TABLE 1                                                         ______________________________________                                                     Free Rise Foam Height (cm)                                                          25     50   100  150  200  350                             Catalyst Amount    sec    sec  sec  sec  sec  sec                             ______________________________________                                        0.8 DABCO                                                                              1.04 g    2.54   8.13 21.6 25.7 25.1 24.4                            33-LV                                                                         0.5 DABCO                                                                              0.65 g    2.29   3.56  9.40                                                                              15.2 18.5 21.6                            33-LV                                                                         Example 1                                                                              0.69 g    2.29   4.32 12.2 19.1 22.9 24.1                            Zwitterion.sup.a                                                              0.5 DABCO                                                                              0.65 g                                                               33-LV                                                                         Example 4                                                                              0.67 g    2.54   4.57 12.2 19.3 23.6 25.4                            Zwitterion.sup.b                                                              0.5 DABCO                                                                              0.65 g                                                               33-LV                                                                         ______________________________________                                         .sup.a 33 wt % dissolved in dipropylene glycol                                .sup.b 29 wt % dissolved in diethylene glycol                            

These data clearly show the delay in foam rise for the zwitterioncatalyzed foams. These foams are comparable in rise height vs time tothe 0.5 pphp DABCO 33-LV catalyst control foam for approximately thefirst minute. After this period, the rise height vs time is acceleratedfor the zwitterion containing foams. In fact, the zwitterion containingfoams achieve maximum heights which surpass that of the 0.5 pphp DABCO33-LV catalyst foam and are comparable to the 0.8 pphp DABCO 33-LVcatalyst foam.

EXAMPLE 7

A more general and quantitative technique for measuring catalystactivity is given in this example. Here the relative catalytic activityof Examples 1 and 3-5 zwitterions is compared with a control catalyst,triethylenediamine. Reactivity data for an uncatalyzed run is alsoincluded. The rate of isocyanate consumption as a function of time wasmeasured using a formulation similar to that of Example 6, butcontaining monofunctional reactants. Reaction samples drawn at theindicated times were quenched with dibutylamine and analyzed by liquidchromatography. The catalysts were compared on an equimolar basiscorresponding to a loading of 0.35 pphp DABCO 33LV catalyst in an actualfoam. Table 2 summarizes the results.

                  TABLE 2                                                         ______________________________________                                                  % NCO Conversion                                                    CATALYST/                                                                     TIME (min)  0.5    1.0    2.0  3.0  4.0  6.0  8.0                             ______________________________________                                        Uncatalyzed 4.0    8.5    17.6 29.1 35.8 49.4 57.8                            Triethylenediamine                                                                        14.2   28.9   50.3 64.1 71.6 79.9 83.6                            Example 1   5.5    10.5   20.4 35.2 64.3 83.6 89.5                            Zwitterion                                                                    Example 3   4.4    7.2    20.2 37.1 54.8 71.3 77.7                            Zwitterion                                                                    Example 4   4.3    8.8    29.0 88.0 90.6 92.0 93.6                            Zwitterion                                                                    Example 5   4.1    8.5    20.0 83.7 93.4 93.4 93.9                            Zwitterion                                                                    ______________________________________                                    

These data show the quaternary ammonium carboxylate zwitterions to berelatively inactive during the early stages of the polyurethane formingprocess. In fact, the %NCO conversions resemble those obtained withoutcatalysis for at least the first minute of reaction time. Surprisingly,these materials all become active between 1 and 3 min of reaction time.Example 1, Example 4, and Example 5 zwitterions are unexpectedly activeafter the initial dormant period.

EXAMPLE 8

This example shows the minimum achievable pull time (indication of cure)for microcellular foams prepared using Example 2 and Example 4zwitterions in combination with triethylenediamine. Polyurethanepremixes were prepared according to Table 3.

                  TABLE 3                                                         ______________________________________                                                  Premix 1 Premix 2   Premix 3                                        ______________________________________                                        Desmophen 2001                                                                            90.5   wt %    90.3 wt %  90.3 wt %                               KS (polyol)                                                                   Water       0.42   wt %    0.42 wt %  0.42 wt %                               LK 221 (surfactant)                                                                       0.42   wt %    0.42 wt %  0.42 wt %                               Ethylene Glycol                                                                           6.54   wt %    6.06 wt %  6.35 wt %                               (chain extender)                                                              DABCO EG    2.21   wt %    1.9  wt %  1.9  wt %                               (33 wt % TEDA                                                                 in DEG)                                                                       Example 2                             0.64 wt %                               Zwitterion                                                                    Example 4                  0.91 wt %                                          Zwitterion.sup.a                                                              ______________________________________                                         .sup.a 33 wt % dissolved in ethylene glycol                              

The control catalyst formulation (Premix 1) contained only DABCO EGcatalyst. For zwitterion catalyzed foams, 10 wt% of the DABCO EGcatalyst in the control formulation was replaced with the test catalyst.A correction in DABCO EG catalyst level was made in Premix 3 to accountfor the excess triethylenediamine contained in Example 2 zwitterion.Ethylene glycol was adjusted to a total of 7.9 wt% in each formulation.Foams were prepared from 105° C. premix and 108° C. diphenylmethanediisocyanate (Mondur E-501) using DESMA PSA53 mixing equipment. The NCOindex at which minimum pull time could be achieved was determined ineach case. Table 4 shows pull time vs index for each formulation.

                  TABLE 4                                                         ______________________________________                                                Pull Time (sec)                                                       NCO Index Premix 1     Premix 2 Premix 3                                      ______________________________________                                         91       95 sec                                                               96       85 sec       80 sec                                                 100       80 sec                                                              102       130 sec                                                             105                    80 sec                                                 110                    45 sec   65 sec                                        114                    25 sec   50 sec                                        119                    20 sec   65 sec                                        125                    60 sec                                                 ______________________________________                                    

These data show that the minimum achievable pull time was improved whena portion of the control catalyst was substituted with the Example 2 andExample 4 zwitterions. With the control (Premix 1), a minimum pull timeof less than 80 sec could not be achieved and, in fact, pull timeincreased dramatically above 100 NCO index. In contrast, the NCO indexof the zwitterion containing foams could be increased substantiallyabove 100 with a concommitant and substantial decrease in pull time (to20 sec at 119 NCO index for Premix 2, Example 4 zwitterion; 50 sec at114 NCO index for Premix 3, Example 2 zwitterion).

STATEMENT OF INDUSTRIAL APPLICATION

The present invention provides quaternary ammonium carboxylate innersalt compositions for use as controlled activity catalysts in makingpolyurethane foams.

We claim:
 1. In a method for catalyzing the trimerization of anisocyanate and/or the reaction between an isocyanate and a compoundcontaining a reactive hydrogen, the improvement which comprisesemploying as a catalyst composition a quaternary ammonium carboxylateinner salt.
 2. The method of claim 1 in which the quaternary ammoniumcarboxylate inner salt has the following formula I: ##STR9## where R₁,R₂ and R₃ are independently C₁ -C₁₂ alkyl, C₅ -C₈ cycloalkyl , C₆ -C₁₀aryl or such alkyl, cycloalkyl or aryl group containing a heteroatom,or;R₁ and R₂, or R₁, R₂ and R₃ together with the nitrogen atom form anitrogen containing ring system; and R₄ is a divalent R₁.
 3. The methodof claim 2 in which R₁, R₂ and R₃ are independently methyl, ethyl,propyl, butyl, lauryl, N,N-dimethylaminoethyl, N,N-dimethylaminopropyl,cyclopentyl, cyclohexyl, phenyl or p-tolyl.
 4. The method of claim 2 inwhich R₁ and R₂ together with the nitrogen atom comprise piperidine,morpholine or imidazole.
 5. The method of claim 2 in which R₁, R₂ and R₃comprise triethylenediamine, 3-quinuclidinol or1,8-diazabicyclo-[5.4.0]undec-7-ene.
 6. The method of claim 2 in whichR₁, R₂ and R₃ comprise triethylenediamine.
 7. The method of claim 2 inwhich R₄ is methylene, ethylene, propylene or phenylene.
 8. The methodof claim 3 in which R₄ is methylene, ethylene, propylene or phenylene.9. The method of claim 4 in which R₄ is methylene, ethylene, propyleneor phenylene.
 10. The method of claim 5 in which R₄ is methylene,ethyleneor propylene.
 11. The method of claim 6 in which R₄ ismethylene, ethylene or propylene.